JP2005021682A - X-ray generator for ct system and slip ring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To feed an electric power efficiently to a rotatable X-ray tube (17) that generates an X-ray beam in order to collect CT data. <P>SOLUTION: This apparatus comprises a slip ring (56) and transmits the electric power from a fixed inverter to a rotatable HV tank (50). The HV tank (50) adjusts the transmitted electric power and generates an electric potential in the X-ray tube (17) for generating an X-ray. The inverter has one or a pair of series resonant circuit (62) connected to the slip ring directly or indirectly via a transformer (70), limits frequency components, reduces voltage common mode components and electric current waveforms transmitted by the slip ring (56), and reduces a loss of electric power. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates generally to diagnostic imaging systems using computed tomography, and more particularly, a fixed inverter supplies power to a slip ring and transmits it to a rotating high voltage tank to generate potentials at both ends of the rotating X-ray tube. The present invention relates to an X-ray generator and a slip ring for a CT system.

  Typically, in a computed tomography (CT) imaging system, an x-ray source emits a fan beam toward a subject or object such as a patient or baggage. Hereinafter, the terms “subject” and “object” shall include anything that can be imaged. The beam impinges on the array of radiation detectors after being attenuated by the subject. The intensity of the attenuated radiation beam received at the detector array is usually determined by the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal that represents the attenuated beam received by each detector element. The electrical signal is sent for analysis to a data processing system that ultimately produces an image.

  In general, the x-ray source and detector array are in the imaging plane and rotate around the gantry surrounding the subject. An x-ray source typically includes an x-ray tube and emits an x-ray beam at a focal point. An X-ray detector typically receives a collimator that collimates the X-ray beam received by the detector, a scintillator that is adjacent to the collimator and converts X-rays into optical energy, receives light energy from the adjacent scintillator, and from there. A photodiode for generating a signal.

  Usually, each scintillator of the scintillator array converts X-rays into light energy. Each scintillator emits light energy to the photodiode adjacent to it. Each photodiode detects light energy and generates a corresponding electrical signal. The output of the photodiode is then sent to the data processing system for image reconstruction.

  The x-ray generator of the CT system is placed in the gantry as rotating around the imaging bore during data acquisition. An x-ray generator typically includes an x-ray tube, a data acquisition system, and an arc detector array. This known configuration is shown in FIG. As shown, the X-ray generator and slip ring configuration 2 includes an X-ray tube 3, a high voltage (HV) tank 4, and an inverter 5 operatively connected to the slip ring 6. The X-ray tube 3, the HV tank 4, and the inverter are respectively connected and fixed to a rotation base 7 that supports each of the gantry during rotation. Outside the rotating base 7, electrically connected to the slip ring 6 is a power distribution unit (PDU) 8, which is stationary and therefore does not rotate with the X-ray tube 3, the tank 4 and the inverter 5. . The inverter 5 is usually supplied with a DC voltage of, for example, 650 VDC, and generates an AC voltage waveform of about 300 VAC, for example, at a specific frequency, that is, 20 k to 50 kHz. The alternating voltage is then supplied to the HV tank 4, which has a transformer and a rectifier (not shown) that generate a direct HV potential. Next, the HV potential is applied to the X-ray tube 3. Since the HV tank and inverter are located on the rotating base, power to the inverter is easily transmitted across the relatively low voltage (˜650 VDC) slip ring 6 to the rotating side. The rotating base 7 is also designed with one or more auxiliary devices that can include an auxiliary power device, typically represented by 4A.

  With this configuration, the inverter 5 is arranged on the rotary base 7 and thus rotates during data collection. A circuit diagram of the inverter is shown in FIG. Inverter 5 includes several power switches 9 (eg, IGBTs) arranged in an H-shaped configuration. Connected to one output of the H configuration is an LC circuit that forms the resonant circuit 10. The output of the resonance circuit 10 and the other output of the H-type configuration 9 are supplied to the HV tank 4. The HV tank includes a transformer 11 connected to a rectifier and filter circuit 12 and generates a potential to the monopolar X-ray tube 3. The inverter 5, the HV tank 4, and the X-ray tube 3 are positioned on the rotation side of the slip ring 6. As a result, using this known configuration, a relatively low DC voltage is supplied to the slip ring 6 and then transmitted to the inverter 5 for adjustment.

  The arrangement of the inverter on the rotating side of the slip ring has several drawbacks. For example, rotating the gantry at a higher speed is problematic because the mass of the rotating component as well as the associated rotational force limits the gantry speed. Further, as the gantry speed increases, the power required for the X-ray generator to maintain a constant SNR (signal to noise ratio) increases as well. Therefore, the size and mass of the x-ray generator components must also be increased to provide the required power. Further, the size of the X-ray generator components in modern CT systems results in a cantilever configuration that protrudes from the rotating base. This cantilever configuration not only applies torque to the mounting bracket used to fix the components, but also increases the force on the fixing bracket. All of these limit the rotational speed of the gantry.

  Thus, an x-ray generator architecture that reduces the size and weight constraints on the rotating base of the CT system, thereby allowing the gantry rotation speed to be increased without losing power transmitted to the x-ray tube. Design is desired.

  The present invention relates to an apparatus for supplying power to an X-ray tube that generates an X-ray beam for CT data acquisition that overcomes the aforementioned drawbacks. The apparatus includes a slip ring designed to transfer power from a fixed inverter to a rotatable HV tank. The HV tank is designed to regulate the power transmitted and cause the X-ray tube to generate a potential for X-ray generation. Furthermore, the inverter is configured to have a single series resonant circuit or a pair of series resonant circuits that are connected directly to the slip ring or indirectly through a transformer.

  Thus, according to one aspect of the present invention, an x-ray generator for a CT scanner includes a slip ring, and a rotary high voltage tank and a rotation operatively connected to the slip ring to receive power from the high voltage tank. Transmit power to and from possible x-ray tubes. The x-ray tube is also configured to project x-rays toward an object to be scanned located in the scan section. The x-ray generator also includes a fixed inverter and supplies alternating current power to the slip ring for transmission to the high voltage tank.

  According to another aspect of the present invention, a CT imager includes a rotatable gantry having an imaging bore disposed therethrough and a fixed base that supports the gantry. The slip ring is placed in a rotatable gantry and is electrically connected to the x-ray tube and the high voltage tank. The high voltage tank is designed to apply a high voltage potential to the X-ray tube for generating X-rays for data collection. The CT imager also includes a power regulator external to the gantry to receive a DC voltage and generate an AC voltage waveform that is applied to the high voltage tank through the slip ring.

  According to another aspect of the invention, a CT scanner includes an x-ray tube and a high voltage tank. The high voltage tank is configured to apply a high voltage potential to the x-ray tube. The CT scanner also includes a slip ring and transmits current to the high voltage tank. A fixed base having an inverter and supplying AC power to the slip ring for transmission to the high voltage tank is also disclosed. The inverter includes at least one resonant circuit connected to the slip ring.

  Various other features, objects, and advantages of the invention will be made apparent from the following detailed description and the drawings.

  The following drawings represent one preferred embodiment that is intended to practice the invention.

  With reference to FIGS. 3 and 4, a computed tomography (CT) imaging system 14 is shown as including a representative rotatable gantry 15 of a “third generation” CT scanner. The gantry 15 is positioned in the gantry support 16 and has an x-ray tube 17 that projects an x-ray beam 18 toward a detector array 19 on the opposite side of the gantry 15. The gantry 15 is designed to rotate and is therefore defined as the rotating side, while the support 16 does not rotate and is therefore defined as the stationary side. A slip ring (not shown) is positioned adjacent to a rotating base (not shown) for transmitting current to the rotating x-ray generator component during data acquisition. The rotating base is designed to support the x-ray tube 17, high voltage (HV) tank (not shown), and other auxiliary components (not shown) while rotating around the medical patient 22. As will be described in detail below, the slip ring is configured to transmit power received from a gantry support or a fixed inverter (not shown) in the base to the HV tank, thereby transferring the potential to X-rays. It can be applied to the tube 17. It will be apparent to those skilled in the art that the present invention is also applicable to the projection and detection of gamma radiation and other high frequency electromagnetic energy.

  The detector array 19 is formed by a plurality of detectors 20 that sense together the projected X-rays that pass through the medical patient 22. Each detector 20 generates an electrical signal representing the impact intensity of the x-ray beam and the attenuated beam as it subsequently passes through the patient 22. During the scan for x-ray projection data collection, the gantry 12 and components attached thereto rotate about the center of rotation 24.

    The rotation of the gantry 15 and the operation of the X-ray source 17 are controlled by the control mechanism 26 of the CT system 14. The control mechanism 26 includes an X-ray controller 28 that supplies power and timing signals to the radiation source 17, and a gantry motor controller 30 that controls the rotational speed and position of the gantry 15. A data acquisition system (DAS) 32 of the control mechanism 26 samples the analog data from the detector 20 and converts the data to digital signals for subsequent processing. An image reconstructor 34 receives the sampled and digitized x-ray data from the DAS 32 and performs high speed image reconstruction. The reconstructed image is used as an input to a computer 36 that stores the image in the mass storage device 38.

  Computer 36 also receives commands and scanning parameters from the operator via console 40 that has a keyboard. The associated cathode ray tube display 42 allows the operator to observe the reconstructed image and other data from the computer 36. The commands and parameters provided by the operator are used by the computer 36 to provide control signals and information to the DAS 32, X-ray controller 28, and gantry motor controller 30. Further, the computer 36 operates a table motor controller 44 that controls the electric table 46 to position the patient 22 and the gantry 15. In particular, the table 46 moves a portion of the patient 22 through the gantry opening 48.

  Referring to FIG. 5, an X-ray generator and slip ring configuration according to the present invention is shown. X-ray generator and slip ring arrangement 48 includes a high voltage tank connected to X-ray tube 17 and rotating base 52. The rotating base 52 is located in the gantry of the CT system and is designed to support the rotational movement of the X-ray tube 17 and the high voltage (HV) tank 50. Similarly, the auxiliary device 54 is also supported by the rotation base 52. The HV tank 50 is designed to convert an AC signal and generate a high voltage DC voltage that can be applied to the X-ray tube 17. For example, in one embodiment, the HV tank 50 is designed to generate a potential of up to 160 kV for application to the x-ray tube 17. The x-ray tube generates x-rays that are projected as a function of the voltage applied here towards the patient being scanned.

  Configuration 48 also includes a slip ring schematically illustrated by arc 56, which is designed to transmit current to HV tank 50 in a generally annular shape. In this regard, the slip ring 56 is designed to receive an alternating voltage waveform from a power distribution unit (PDU) 58. As shown, the PDU 58 can include an inverter 60 designed to provide an alternating waveform to the slip ring 56. However, those skilled in the art will appreciate that the inverter can be located outside the PDU. As will be discussed in further detail below, the inverter 60 is fixed with respect to the rotating components of the configuration 48 so that it does not rotate around the patient during data acquisition. Further, in one embodiment, the inverter 60 is designed to supply an AC waveform up to 300V to the slip ring 56 at a frequency of 30 kHz. One skilled in the art will appreciate that other frequency ranges such as about 20k to 1 MHz are also contemplated.

  The slip ring 56 has a relatively large diameter and can therefore function as a radiating antenna. Therefore, to minimize electromagnetic radiation, it is essential to limit the frequency components of the slip ring current and voltage waveform. For this purpose, as shown in FIG. 6, the present invention includes an inverter topology for limiting the frequency components of the waveform transmitted to the slip ring. Inverter 60 includes a pair of resonant circuits 62. Each resonant circuit includes a capacitor C and an inductor L (connected in series?). Each resonance circuit 62 is connected to the outputs of a plurality of power switches 64 arranged in an H-type configuration. The power switch can include a MOSFET, an IGBT, or the like. The power switch 64 is designed to receive a high voltage DC input, such as 650 VDC, and generate an AC voltage at a variable frequency, ie, about 20 to 100 kHz.

  The resonant circuit is connected to the output of the power switch configuration and is therefore located between the power switch output and the slip ring 56. Note that in one embodiment, the values of the inductance component and reactance component of the resonant circuit are the same for each converter. The resonant circuit is designed to smooth out the fast transitions of the power switch, thereby limiting the frequency component and reducing the common mode component of the waveform transmitted to the slip ring 56.

  Still referring to FIG. 6, the slip ring 56 delimits the stationary and rotating sides of the X-ray generator. As described above, the inverter and its associated topology are located on the stationary side of the slip ring 56. Therefore, the inverter does not rotate with the high voltage tank 50 or the X-ray tube 17 during the data collection process. The rotating side and slip ring configuration of the X-ray generator includes an HV tank 50 that receives the AC waveform from the slip ring 56 and adjusts the waveform to provide a high voltage DC potential to the X-ray tube 17. Designed as such. The HV tank 50 includes a transformer 66 and a rectifier and filter circuit 68 that regulates the AC voltage signal transmitted by the slip ring 56. In the exemplary embodiment, the HV tank 50 is designed to apply a 160 kV DC potential to the X-ray tube 17.

Referring now to FIG. 7, an inverter topology according to another embodiment of the present invention is shown. In this embodiment, the inverter 60 is similar to the topology described with respect to FIG. 6 and is arranged in an H-type configuration designed to output an alternating voltage waveform smoothed by a pair of series resonant circuits 62. Several power switches. However, unlike the topology shown in FIG. 6, the configuration shown in FIG. 7 includes a transformer disposed between the resonant circuit output and the slip ring 56. The transformer 70 is incorporated into the configuration to control the effective inductance of the slip ring 56. For example, the slip ring 56 typically has an inductance in the range of 0.2 mH to 0.6 mH depending on the rotational position. By adding transformer 70 into the circuit, the effective inductance is reduced to N ² , where N is the turns ratio of transformer 70. For example, when the turns ratio of the transformer 70 is 1: N, the inductance or fluctuation of the slip ring 56 is reduced to 1/25, for example, from 0.4 mH to 0.016 mH. Furthermore, the slip ring has a series resistance that is also reduced to N ² , thereby reducing losses.

The transformer 70 incorporated in the X-ray generator and slip ring configuration with a 1: N turns ratio needs to reduce the turns ratio of the transformer 66 and the HV tank 50 to N in order to compensate for the inclusion of the transformer 70. is there. That is, the turns ratio of the transformer 66 is 1: X-N, where N is the turns ratio of the transformer 70 and X is the turns ratio of the transformer 66 without the transformer 70 in the system. . For example, if transformer 66 has a turns ratio of 8 in another situation without transformer 70, incorporating transformer 70 with a turns ratio of 5 requires transformer 66 to be configured to have a turns ratio of 3. Will. Furthermore, the slip ring has an effective inductance of Y / N ² , where Y corresponds to the inductance of the slip ring without the transformer 70 included in the circuit topology.

  With the above-described invention, when the inverter assembly and its associated bracket are removed from the rotating side, they have the same weight as the inverter assembly and then have a counterweight normally attached to the CT system that can then be removed. be able to. The relocation of the inverter to the stationary side of the system, and the removal of any counterweight, makes it possible to eliminate any cantilever configuration, providing a more evenly balanced gantry, It is indispensable for speeding up the gantry speed of 2 seconds / rotation. In addition, the high frequency alternating current waveform of the slip ring allows a non-contact slip ring, which eliminates the slip ring brush. In addition, by rearranging the inverter from the rotating side of the system to the stationary side, large generators can be used in the laboratory to generate high power levels such as 150 kW and 200 kW that are usually required for high-speed scanning. Become.

  Referring now to FIG. 8, an X-ray generator and slip ring configuration according to another embodiment of the present invention is shown. The configuration of FIG. 8 is similar to the embodiment of FIG. 7, however, the configuration of FIG. 8 uses only a single series resonant circuit 62. In this regard, one output of the H configuration of the power switch 64 is supplied to the resonant circuit 62 and the other output is connected directly to the transformer 70. The output of the resonant converter 62 is also supplied to the transformer 70. Therefore, the positive part of the AC waveform output by the power switch is supplied to the resonance circuit and smoothed, while the negative part of the AC waveform is supplied directly to the transformer 70. Similar to the embodiment of FIGS. 6 and 7, the inverter 60 is fixed, and the HV tank 50 and the X-ray tube 17 rotate. The current passed through the slip ring 56 by the transformer 70 is transmitted to the HV tank 50 and generates a high voltage potential applied to the X-ray tube 17 that generates X-rays for CT data collection. Similar to the configuration shown in FIG. 7, the turns ratio of the transformer 70 in FIG. 8 affects the turns ratio of the transformer 66 in the HV tank 50. In addition, high frequency components and common mode components on the slip ring waveform are also reduced.

  Referring now to FIG. 9, a luggage / baggage inspection system 100 that incorporates an x-ray generator and slip ring architecture and the topology of the present invention described above includes a rotatable gantry 102 with an opening 104 therein. Baggage or baggage can pass through. The rotatable gantry 102 houses a high frequency electromagnetic energy source 106 as well as a detector assembly 108. A conveyor system 110 is also provided and includes a conveyor belt 112 that is supported by the structure 114 and that automatically and continuously passes the load or baggage 116 to be scanned through the opening 104. The object 116 is fed through the opening 104 by the conveyor belt 112 and then imaging data is collected and the conveyor belt 112 moves the load 116 from the opening 104 in a controlled and continuous manner. As a result, postal inspectors, baggage handlers, and other security personnel can non-invasively inspect the contents of luggage 116 for explosives, knives, guns, smuggled goods, and the like.

  Thus, according to one embodiment of the present invention, an X-ray generator for a CT scanner is electrically connected to a slip ring that transmits power to a rotating high voltage tank and to receive power from the high voltage tank. A rotatable X-ray tube connected to the X-ray tube. The x-ray tube is configured to project x-rays toward an object to be scanned located in the scan section. The x-ray generator also includes a fixed inverter and supplies alternating current power to the slip ring for transmission to the high voltage tank.

  According to another embodiment of the present invention, a CT imager includes a rotatable gantry having an imaging bore disposed therethrough and a fixed base that supports the gantry. The slip ring is placed in a rotatable gantry and is electrically connected to the x-ray tube and the high voltage tank. The high voltage tank is designed to apply a high voltage potential to an X-ray tube that generates X-rays for data collection. The CT imager also includes a power regulator external to the gantry to receive a DC voltage and generate an AC voltage waveform that is applied to the high voltage tank via a slip ring.

  According to another embodiment of the invention, the CT scanner includes an x-ray tube and a high voltage tank. The high voltage tank is configured to apply a high voltage potential to the X-ray tube. The CT scanner also includes a slip ring to transmit current to the high voltage tank. Also disclosed is a fixed base having an inverter for supplying AC power to the slip ring for transmission to a high voltage tank. The inverter includes one or a pair of resonant circuits connected to the slip ring either directly or through a transformer.

  Although the invention has been described with reference to preferred embodiments, it is understood that equivalents, alternatives, and modifications are possible and fall within the scope of the appended claims, unless explicitly stated.

1 is a schematic diagram of a known X-ray generator and slip ring configuration of a CT imaging system. FIG. 2 is a schematic circuit diagram of a known inverter topology for using the configuration shown in FIG. 1. 1 is a perspective view of a CT system according to one embodiment of the present invention. FIG. 2 is a block schematic diagram of the system shown in FIG. 1 is a schematic diagram of an X-ray generator and slip ring configuration according to one embodiment of the present invention. FIG. 6 is a circuit diagram of the inverter topology of the configuration shown in FIG. 5 according to another embodiment of the present invention. 6 is a circuit diagram of an alternative inverter topology for the configuration shown in FIG. 5 according to yet another embodiment of the invention. 6 is a circuit diagram of another inverter topology for the configuration shown in FIG. 5 according to another embodiment of the present invention. FIG. 3 is a perspective view of a CT system for use with a non-invasive package inspection system.

Explanation of symbols

17 X-ray tube 50 High voltage tank 56 Slip ring 60 Inverter 62 Resonant circuit 64 Power switch 66 Transformer 68 Filter circuit

Claims (8)

An X-ray generator (14) for a CT scanner;
A slip ring (56) for transmitting power to a rotating high voltage (HV) tank (50);
A rotatable X-ray tube (operatingly connected to the slip ring (56), receiving power from the HV tank (50) and projecting X-rays onto the subject (22) to be scanned ( 17)
A fixed inverter that supplies AC power to the slip ring (56) for transmission to the HV tank (50);
An X-ray generator comprising:   The fixed inverter includes a number of power switches (64) arranged in an H-bridge configuration, said configuration including a pair of outputs, at least one of the outputs being connected to a resonant circuit (62) The X-ray generator according to claim 1.   X-ray generator according to claim 2, characterized in that at least one resonant circuit (62) is connected to a slip ring (56).   The X-ray generator according to claim 3, wherein each resonance circuit includes a capacitor and an inductor connected in series.   The at least one resonant circuit (62) is connected to an input of a transformer (70), the transformer (70) having an output connected to a slip ring (56). X-ray generator.   The transformer (70) has a 1: N turns ratio and the transformer (66) of the high voltage tank (50) has a 1: X-N turns ratio. The described X-ray generator. X-ray generator according to claim 6, wherein the slip ring (56) is characterized by having an effective inductance of the Y / N ^2.   X-ray generator according to claim 1, incorporated in a CT imager (14) having a rotatable gantry (15).

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